1. field of the Invention
The invention is directed to a method of operating a drive unit comprised of an internal combustion engine with a hydraulic aggregate group connected to it. The amount of fuel supplied to the engine in the upper idling speed range is limited by a proportional operating speed control. The power consumption of the hydraulic aggregate group is reduced by a maximum load regulator when the engine is overloaded. After the engine speed decreases below an arbitrary prescribed rated RPM, which is monitored by the maximum load regulator, the hydraulic aggregate group is shifted toward a lower power consumption.
Such methods are known and described, for example, in Federal Republic of Germany Patent No. DE-OS 3 21 636. In order to utilize the maximum power of the engine without overloading it, maximum load regulation is provided to monitor the power consumption of the hydraulic aggregate group connected to the engine by comparing the actual RPM of the engine with the prescribed rated RPM, e.g., the nominal speed, and when the engine is overloaded, i.e., when the ac drops below the arbitrarily prescribed rated RPM, emits a signal on the basis of which the power-consuming hydraulic aggregate group is regulated so that the power consumption does not exceed the power output capacity of the engine. The arbitrarily prescribed RPM, which in most cases is the nominal speed of the internal combustion engine, represents the working RPM of the maximum load regulation of the engine. When the engine is not loaded, its actual RPM rises above the rated RPM up to the upper idling speed. The range between the rated RPM (normally the nominal speed) and the upper idling speed is designated as the idling control characteristic at which the amount of fuel injected in a diesel engine, for example, is reduced by centrifugal regulation to prevent the engine from operating overspeed.
In power machines, such as dredges, it is frequently desirable to limit the power of the overall drive unit to a value below the nominal power for certain applications. There are a number of hydraulic circuits for this purpose known as power limiters. In order to obtain a stepped-variable power limitation, a change-over of the hydraulic-mechanical parameters can generally be undertaken. Such circuits and apparatuses are expensive.
The present invention avoids the above noted shortcoming and offers a method of operating a drive unit comprised of an engine and a hydraulic aggregate group connected to it which facilitates a variable power limitation without a hydraulic power limiter.